Schaffer wrote several episodes of the sitcom Seinfeld. He also served as executive producer during its ninth season. He has also held various other positions on the show such as program consultant, supervising producer and story editor.

Schaffer directed several episodes of Curb Your Enthusiasm and also served as executive producer for several episodes. Notably, Schaffer directed the finale episode of the seventh season, titled "Seinfeld", which featured a reunion of the original cast of Seinfeld.